The present invention relates to a waveform signal generation method, a waveform signal generation apparatus and a storage medium used for an apparatus generating a musical tone signal such as an electronic instrument a portable phone, an amusement machine and others. In particular, the present invention relates to a waveform signal generation method, a waveform signal generation apparatus and a storage medium which are preferable for use in a compact device among these devices.
In an electronic instrument, a portable phone, an amusement machine and others, a musical tone signal is sounded through a built-in or external electo-acoustic converter (speaker and the like). Here, a range of sounds which can be converted has a predetermined limit. In particular, as to a low note, only sounds above a lowest frequency (which will be referred to as a xe2x80x9clowest frequencyxe2x80x9d or a xe2x80x9creproducible lowest frequencyxe2x80x9d hereinafter) specified by a lowest resonance frequency of the electo-acoustic converter can be sounded.
In order to solve this problem, there is known a technique for generating a xe2x80x9cpseudo low tonexe2x80x9d. This is a technique utilizing an illusion of human sense such that generating audio signals having given two frequencies enables a human to hear a signal corresponding the greatest common factor of these frequencies. For example, in order to generate the xe2x80x9cpseudo low tonexe2x80x9d having 100 Hz by a speaker which cannot output an audio signal having 100 Hz, generation of two frequencies whose greatest common factor is 100 Hz, for example, xe2x80x9c200 Hz and 300 Hzxe2x80x9d, xe2x80x9c300 Hz and 400 Hzxe2x80x9d and others can suffice.
For example, U.S. Pat. No. 5,930,373 discloses this technique in detail. According to this technique, in digital audio signals sequentially supplied, filtering process is applied to components which cannot be reproduced by the speaker, and a frequency component which is twofold, threefold, . . . of these frequency components is generated. The thus generated frequency components and the original audio signal are mixed with each other to be sounded through the speaker.
In the technique disclosed in the above-described U.S. patent, however, since processing such as multiplication must be executed in accordance with each sampling cycle with respect to the sequentially supplied digital audio signal, a large volume of calculations are required in order to generate a pseudo low tone. In an electronic instrument and the like, since diverse kinds of processing must be performed besides generation of the pseudo low tone, the throughput capacity allocated for generation of the pseudo low tone itself has a limit.
In view of the above-described problems, it is an object of the present invention to provide a waveform signal generation method, a waveform signal generation apparatus and a storage medium for reducing a processing load required for generating a pseudo low tone. It is another object of the present invention to provide an audio signal generation method, an audio signal generation apparatus and a storage medium capable of generating a pseudo low tone in a natural state.
In order to solve the above-described problems, the present invention comprises the following structure. Namely, there is provided a method of generating waveform signals from a plurality of channels to sound a music tone through an electro-acoustic converter in response to sounding instruction information. The inventive method is carried out by a receipt process of receiving the sounding instruction information containing a designated pitch effective to specify a pitch of the music tone, a determination process of determining whether or not the designated pitch is lower than a critical pitch which is predetermined in association with the electro-acoustic converter, a first generation process of generating a first waveform signal containing a fundamental tone corresponding to the designated pitch at least when the determination process determines that the designated pitch is not lower than the critical pitch, and a second generation process of generating a second waveform signal containing at least two overtones which are multiples of the fundamental tone and higher than the critical pitch, only when the determination process determines that the designated pitch is lower than the critical pitch, thereby the second waveform signal providing a pseudo low tone below the critical pitch.
Preferably, the first generation process generates the first waveform signal from a first channel even when the determination process determines that the designated pitch is lower than the critical pitch, and concurrently the second generation process generates the second waveform signal from a second channel different than the first channel, so that the first waveform signal and the second waveform signal are mixed with each other to provide the music tone containing the pseudo low tone.
Preferably, the first generation process generates the first waveform signal by reading out first prestored waveform data and the second generation process generates the second waveform signal by reading out second prestored waveform data, the method further comprising a mix process of mixing the first waveform signal and the second waveform signal with each other when the determination process determines that the designated pitch is lower than the critical pitch, thereby providing the music tone containing the pseudo low tone.
Preferably, the first generation process does not generate the first waveform signal when the determination process determines that the designated pitch is lower than the critical pitch, while the second generation process generates the second waveform signal containing the first waveform signal as well as the overtones, thereby providing the music tone containing the pseudo low tone.
Preferably, the first generation process generates the first waveform signal by reading out first waveform data which is prestored and the second generation process generates the second waveform signal by reading out second waveform data which is a mixture of the first waveform data and additional waveform data corresponding to the overtones.
Preferably, the first generation process generates the first waveform signal according to a waveform generation algorithm constituted by a plurality of operators, and the second generation process generates the second waveform signal according to another waveform generation algorithm constituted by a plurality of operators, the second generation process generating the overtones through a parallel connections of the operators assigned to the respective ones of the overtones. In such a case, the first generation process generates the first waveform signal by using operators belonging to a first channel, and the second generation process generates the second waveform signal by using operators belonging to a second channel different than the first channel.
There is provided another method of generating first and second waveform signals to output a music tone containing a pseudo low tone audible below a critical pitch. The inventive method is carried out by a generation process of generating the second waveform signal which corresponds to the pseudo low tone and which differs from the first waveform signal corresponding to the music tone, a coefficient generation process of generating a coefficient which gradually decreases in a predetermined pitch range around the critical pitch as a frequency of the second waveform signal increases, a control process of controlling a level of the second waveform signal according to the generated coefficient, and an output process of outputting the second waveform signal concurrently with the first waveform signal, thereby providing the music tone and the pseudo low tone which fades out as a pitch of the music tone rises.
Preferably, the inventive method further includes an allocation process of allocating a channel to the waveform generation process and setting the allocated channel with tone generation parameters corresponding to the first waveform signal, wherein the output process commands the allocated channel to generate the second waveform signal containing the first waveform signal.
Preferably, the waveform generation process comprises the steps of extracting a fundamental tone component from the first waveform signal which are provided sequentially, and generating at least overtone components of the extracted fundamental tone components so as to provide the pseudo low tone.